The invention relates to a speaker unit for automotive vehicles and more particularly to a composite speaker unit for automotive vehicles.
Speaker units for automotive vehicles have been markedly improved so as to provide superior sound reproduction. Recently, a composite speaker unit (coaxial speaker unit) has been used for automotive vehicles. The composite speaker unit is made up of several individual speakers similar to speaker systems intended for home use in which the various speakers are adapted to operate in specific ranges of the sound spectrum. Although the characteristics of such a composite speaker unit are excellent, satisfatory results are not obtainable if the composite speaker unit is used in an automobile. This is due primarily to the fact that the mounting position of the speaker unit is restricted in the vehicle because of inherent structural limitations. The speaker unit is normally mounted flush with and below the rear parcel shelf of the vehicle. The rear parcel shelf is usually slightly sloped such that the rear side portion of the shelf is higher than the front side portion. However, the slope of the rear parcel shelf is not sufficient to direct the central axis of the speaker unit toward the front of the vehicle but instead directs it toward a rear window of the vehicle.
Transmission of low-range sound is not very directional. Therefore, there is little modification of the lower portion of the sound spectrum even if the speaker unit is directed upward. On the other hand, transmission of medium-range or high-range sound is rather strongly directional. The medium-range and the high-range sounds reaching the listeners are reflected from the rear window or ceiling of the vehicle. The direction from which the medium-range and the high-range sounds arrive at the listeners' ears does not coincide with the direction to the actual sound source. This remarkably degrades the stereophonic effect if the speaker units for right and left channels are provided in the rear parcel shelf.
However, the following advantage is obtained if the speaker unit is mounted flush with the rear parcel shelf. Since the space of a trunk can be utilized as a speaker box for the speaker unit, it is advantageous in that the low-range sound is well reproduced. Due to the above noted advantage and for the reason that no space as large in volume as the space of the trunk room is available in the passenger compartment of the vehicle, it is general practice to flush mount the speaker unit on the rear parcel shelf.